1. Field of the Invention
The present invention relates generally to genetic sequences and their complementary forms capable of facilitating the modification of a phenotype of a plant. More particularly, the present invention relates to polynucleotide sequences defining B-type MADS box genes, to the proteins encoded thereby, to methods for isolating such polynucleotides and to nucleic acid constructs for the expression thereof. The present invention further provides cells, particularly transformed bacterial or plant cells and to differentiated tissue including whole plants and their progeny comprising cells which contain these nucleic acid constructs or parts of the constructs. Plants and parts of plants, such as flowering and reproductive parts including seeds, also form part of the present invention. The genetic sequences of the present invention may be used inter alia for the production of plants and, in particular, oil palm plants, which have modified phenotypes and/or which exhibit more highly desired characteristics such as, for example, male sterility or plants in which the sex ratio may be manipulated, and for the diagnosis and, preferably, elimination of the mantled phenotype.
2. Description of the Related Art
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.
The architecture of flowers is determined by the activity of a number of homeotic genes, typically containing a conserved MADS box domain. The MADS box is a highly conserved sequence domain found in a family of transcription factors. Most MADS domain factors play a key role in developmental processes. In particular, the MADS box genes of flowering plants are the molecular architects of flower architecture.
In both Arabidopsis thaliana and Antirrhinum majus, two B-type genes have been identified. These genes—also known as organ identity genes—specify petal and stamen development. In Arabidopsis, APETALA3 (AP3) and PISTILLATA (PI) are B-type genes. Mutations in either gene disrupt the specification of petal and stamen identity, thereby converting the petals in the second whorls to sepals, and stamens in the third whorl into carpels. Both genes are part of a large family of MADS-box genes that play a central role in the development of flowers. In Antirrhinum, DEFICIENS (DEF) and GLOBOSA (GLO) are B-type genes and together they also control development of petals and stamens. Mutant analysis and binding studies suggest that, in these species, the B-type genes are functional as a heterodimer in specifying the B-function. Consequently, changes in expression in any of the two genes may affect the B-type activity, and hence the organ identity of the second and/or third whorl.
The MADS box gene concept appears to apply to a wide range of plant species, including monocotyledons and trees, with minor adjustments. Notably, in some species more than two B-type genes have been tentatively identified. In Norway spruce, for example, DAL11, DAL12 and DAL13 are related to B-type genes. However, in this plant, it was found that the B-type genes function as both organ identity genes and meristem identity genes, indicating that they have evolved differently in conifers and angiosperms. Recent results suggest that for proper B-type function, expression of additional MADS box genes from the AGL-like gene family is required (Egea-Cortinez et al., EMBO J. 18: 5370-5379, 1999; Honma and Goto, Nature 409: 525-529, 2001). These MADS box genes code for proteins that interact with the B-type heterodimer complex, forming a ternary complex. This third partner may be essential for transcriptional activation of genes coding for downstream processes.
Monocotyledonous plant species that frequently suffer from the adverse effects of inappropriate and/or incorrect flower development, are the oil palm trees of the species Elaeis guineensis and Elaeis oleifera. Trees of these species, which produce palm oil and palm kernel oil, comprise the highest yielding oil crop in the world. The demand for oil and fats is expected to increase dramatically with the increase in world population. Oil palm plantations were forecast to contribute around a quarter of the world's oil and fats demand by the year 2020 (Rajanaidu and Jalani, In Proceedings of 1995 Palm Oil Research Institute of Malaysia—National Oil Palm Conference.—Technologies in Plantation, The Way Forward, pp. 1-29, 1995).
Of particular concern, therefore, is the fact that mutant plants, exhibiting a so-called “mantled” phenotype, are frequently produced during what are becoming routine procedures used for plantation development and replenishment; namely, micropropagation of oil palm plantlets via somatic embryogenesis and/or organogenesis. Since their inception, micropropagation techniques have been found to produce phenotypic variability through somaclonal variation. In clonal progeny from oil palm plants, approximately 5% have been found to exhibit the abnormal “mantled” flower phenotype. This phenotype is characterized by the feminisation of the third whorl in the flowers of both sexes. Such mantled plants develop abnormally and are frequently sterile, thereby directly affecting oil production. The cause of the mantled phenotype is unknown, and studies of ploidy level and polymorphism have not shown relevant genomic changes.
Due to the increased demand for plantation oil palm and palm oil, there is a concomitant need to increase the quality and yield of palm oil and palm kernel oil. An understanding of the phenomenon that leads to mantling is, therefore, critical. There is also a need to develop diagnostic protocols for mantling and to be able to prevent it from occurring altogether. Furthermore, there is an associated need to be able to rapidly develop new plant/oil characteristics when required.